Spiked Apple Samples Research Articles

Rapid and non-invasive surface-enhanced Raman spectroscopy (SERS) detection of chlorpyrifos in fruits using disposable paper-based substrates charged with gold nanoparticle/halloysite nanotube composites.

Chlorpyrifos is one of the most widely used organophosphate insecticides in agricultural production. Nevertheless, the residues of chlorpyrifos in agricultural by-product seriously threaten human health. Thus, the ultrasensitive detection of chlorpyrifos residues in agri-food products is of great demand. Herein, an AuNP/HNT-assembled disposable paper SERS substrate was prepared by an electrostatic self-assembly method to detect chlorpyrifos residues. The AuNP/HNT paper substrate exhibited high SERS activity, good reproducibility, and long-term stability, which was successfully used for quantitative detection of chlorpyrifos; the detection limit reached 7.9 × 10-9M. For spiked apple samples the calculated recovery was 87.9% with aRSD value of 6.1%. The excellent detection ability of AuNP/HNT paper-based SERS substrate indicated that it will play an important role in pesticide detection in the future. AuNP/HNT assembled disposable paper SERS substrate was prepared by an electrostatic self-assembly method to detect chlorpyrifos residues in fruits.

Polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay for screening of paclobutrazol in fruits

Paclobutrazol (PBZ) is a plant growth regulator (PGR) widely used in fruit and vegetable cultivation. However, due to the severe toxicity of PBZ, a sub-ppm level maximum residue limit (MRL) was established worldwide. Therefore, it is significant to propose a rapid, sensitive and high throughput screening method for monitoring the PBZ residues in foods. In this study, a simple and sensitive indirect competitive Enzyme-linked immunosorbent assay (icELISA) was established for PBZ detection in fruits basing polyclonal antibody. For both economy and pollution prevention, a microwave-solvent-free method was used to synthesize the PBZ hapten with high efficiency. The detection conditions, such as coating antigen concentration, antibody concentration, organic reagent concentration, ionic strength and pH, were optimized. Under the optimized conditions, this method showed high sensitivity and specificity. The detection range is 1.27-138.23 ng/mL, half-maximum inhibition concentration (IC50) is 13.26 ng/mL, and the IC20 was lower than the reported ELISAs for PBZ. Additionally, this method had high accuracy and precision. The recoveries were ranged from 88.78% to 96.80% in PBZ spiked apple samples with RSD below 4%. All the results showed that the polyclonal antibody based icELISA could be useful for PBZ screening in fruit samples.

Molecularly imprinted polymer based on magnetic ionic liquid for solid-phase extraction of phenolic acids

ABSTRACTIn this study, 1-allyl-3-octylimidazolium tetrachloroferrate ionic liquid was first synthesized. Molecularly imprinted polymer was prepared by suspension polymerization using 1-allyl-3-octylimidazolium tetrachloroferrate as functional monomer and chlorogenic acid as template molecule. The polymer was characterized by Fourier transformed infrared spectroscopy and scanning electron microscopy. Thermal stability of the polymer was investigated. The solid-phase extraction method based on magnetic molecularly imprinted polymer was developed for gallic acid, protocatechuic acid, caffeic acid, chlorogenic acid, p-coumaric acid, and ferulic acid. The sample pH, the type and volume of stripping solution, sorbent amount, and extraction time were optimized for phenolic acids. The analysis of phenolic acids after extraction was carried out using high-performance liquid chromatography with UV detection. Limit of detection, limit of quantification, linear range, correlation coefficient, and reproducibilities of within-day and between-day for phenolic acids were determined. The residues of phenolic acids in apple samples were successfully detected by the developed method. Recovery of standard spiked apple samples was ≥81 for all the phenolic acids.

Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile

Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl, methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using three different acetylcholinesterase (AChE) enzymes-AChE from electric eel, and genetically engineered (B394) and wild-type (B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer (PVA-AWP). Each biosensor was tested against the four pesticides. Good operational stability, immobilisation reproducibility, and storage stability were obtained for each biosensor. The best detection limits were obtained with the B394 enzyme for dichlorvos and methylparaoxon (9.6 x 10(-11) and 2.7 x 10(-9) mol L(-1), respectively), the B1 enzyme for carbofuran (4.5 x 10(-9) mol L(-1)), and both the B1 enzyme and the AChE from electric eel for carbaryl (1.6 x 10(-7) mol L(-1)). Finally, the biosensors were used for the direct detection of the pesticides in spiked apple samples.

Method Development and Generation of Profiles for Selected Phenolics from Apple Cultivars Used for Processed Products

ABSTRACT: Profiles of selected phenolic constituents of 2 apple cultivars, Northern Spy and Ida Red, commonly used for processed products were compared. Although chlorogenic acid was the principal phenolic in both cultivars, there were significant quantitative differences. A new solid‐phase extraction (SPE) and high‐performance liquid chromatographic (HPLC) separation using polymeric resins was developed for this experiment. Quantification was by ultra‐violet (UV) absorbance using a diode array detector. The performance of this new method was compared with that of a published liquid‐liquid extraction (LLE) method, based on linearity of detector response, limits of detection, reproducibility of analysis, and recoveries from spiked apple samples.

Study on using I− as heavy atom perturber in cyclodextrin-induced room temperature phosphorimetry

A cyclodextrin induced room temperature phosphorimetry (CD-RTP) for determine β-NOA, which using I− as a heavy atom perturber (HAP) and sodium sulfite as a deoxygenator, was developed. The phosphorescence peak wavelength maxima λex/λem=287/496 521 nm. The analytical curve of β-NOA gives a linear dynamic range of 2.0×10−7–6.0×10−6 mol/l and a detection limit of 4×10−8 mol/l. The relative standard deviation (RSD; n=7) was 3.2% for the 4.0×10−6 mol/l β-NOA in spiked apple samples. The influence of I− concentration on RTP lifetime of β-NOA was studied in detail, the static Stern–Volmer equation for phosphorescence was derived and the luminescence kinetic parameters were calculated. It is found that the relation between I− concentration (x) and RTP lifetime (τ) can be expressed as τ=1.047 e−0.354x and the rate constants of phosphorescence emission kp and non-radiation process ki from T1→S0 were 0.9551s−1 and 0.4276 s−1l−1mol, respectively.

Heavy Atom Induced Room Temperature Phosphorescence Method for the Determination of the Plant Growth Regulator β-Naphthoxyacetic Acid

A simple, selective, and sensitive heavy atom induced room temperature phosphorimetric method (HAI-RTP) is described for the determination of the plant growth regulator β-naphthoxyacetic acid (NOA) in spiked apple samples. A careful selection of the different variables (heavy atom and sodium sulfite) to obtain the phosphorescence signal constitutes the basis of a HAI-RTP method for the determination of NOA. The analytical curve of NOA gives a linear dynamic range of 0−625 ng mL-1 and a detection limit of 30.5 ng mL-1. A recovery of 108.8% was obtained for 500 ng mL-1 NOA in spiked apple samples. Keywords: β-Naphthoxyacetic acid; heavy atom induced room temperature phosphorescence (HAI-RTP)

Amperometric selective biosensing of dimethyl- and diethyldithiocarbamates based on inhibition processes in a medium of reversed micelles

An amperometric tyrosinase electrode has been used for biosensing of dimethyl- and diethyldithiocarbamates based on the inhibition effects of these substances on the catalytic activity of the enzyme. A working medium consisting of reversed micelles, and phenol as the substrate has been used. The tyrosinase electrode was constructed by direct adsorption of the enzyme on the surface of a graphite-disk electrode. Reversible inhibition processes are shown to be involved for ziram, diram and zinc diethyldithiocarbamate. Following a simple regeneration of the enzyme electrode, an acceptable reproducibility for the measurements of the inhibition response was obtained. Experimental variables, such as temperature, phenol concentration and the presence of chloroform, affecting the inhibition processes, were optimized. The type of enzyme inactivation for each inhibitor tested was studied, and the inhibition constants were calculated. Detection limits of 0.074, 1.3 and 1.7 μmol l −1 were achieved for ziram, diram and zinc diethyldithiocarbamate, respectively. Other carbamates belonging to families different from dimethyl- and diethyldithiocarbamates showed no amperometric response at the tyrosinase electrode, except for pyrimidine-derivative carbamates. The developed analytical methodology was applied to determine ziram in spiked apple samples.

HPLC-Electrochemical detection with graphite-poly (tetrafluoroethylene) electrode Determination of the fungicides thiram and disulfiram

The suitability of composite graphite-poly(tetrafluoroethylene) (Teflon) electrodes as amperometric indicator electrodes in HPLC detection is demonstrated. The determination of the fungicides thiram and disulfiram in the presence of ziram has been chosen as an analytical problem. The optimization of working conditions, such as the choice of the organic solvent used in the mobile phase as well as its percentage, the potential applied to the composite electrode, and the time elapsed between mixing the carbamates and the injection, has been accomplished by using the wall-jet flow-cell configuration. The effect of the acetonitrile percentage used in the mobile phase on the retention of thiram, disulfiram, ziram and phenol was evaluated. Resolution up to the baseline can be achieved with 45% acetonitrile. The sensitivity of the determination of thiram and disulfiram in the presence of a constant concentration of ziram is slightly better when using a wall-jet cell; however, the background current is higher, as well as the baseline noise and the time necessary to achieve stabilization of the baseline before the injection. Lower limits of detection for both fungicides, as well as a better repeatability, were obtained when using a thin-layer flow cell configuration. As an application, the determination of thiram in spiked apple samples, at a level of 0.5 mg thiram kg −1 apple, has been carried out with a mean recovery of 97 ± 3% for a significance level of 0.05.

Determination of the plant growth regulator β-naphthoxyacetic acid by micellar-stabilized room temperature phosphorescence

This paper presents a method for the determination of the plant growth regulator β-naphthoxyacetic acid (NOA) by micellar-stabilized room temperature phosphorescence with the surfactant Triton X-100 (TX-100) as the micellar medium, thallium nitrate as the heavy atom and sodium sulphite as the oxygen scavenger. A multivariate optimization approach using the blocked cube star design of central composite was carried out. The analytical curve of NOA gives a linear dynamic range of 0.4–3.0 μg ml −1 and a detection limit of 0.13 μg ml −1. A recovery of 93.6% was obtained for 1 μg ml −1 NOA in spiked apple samples.

Polarization fluoroimmunoassay of the herbicide dichlorprop

A polarization fluorescence immunoassay has been developed for the screening of the herbicide dichlorprop [(f)-2-(2,4-dichlorophenoxy)propanoic acid]. The assay is based on the difference in fluorescence polarization between free and antibody-bound fluoresceinamine-labeled dichlorprop. Antibodies toward dichlorprop were produced by immunizing a rabbit with conjugates of dichlorprop to bovine serum albumin. Polarization measurements were performed by using two spectrofluorometers which use different optic configurations. Calibration curves fitted to an IC50 four-parameter logistic model gives chi-square 10-5. The upper end of the standard curve for polarization fluorescence immunoassay is 0.01 pg/mL and the lower end 100 pg/mL. The method offers good analytical specifications and little crossreactivity against similar compounds. The proposed method is compared with enzyme-linked immunosorbent assay using the same set of reagents. The effectiveness of the method on real samples was checked in spiked apple samples. In the analysis of pesticide residues, immunoassay is rapidly becoming an important technique (Hock, 1989; Jung et al., 1989; Sherma, 1991). Although the development of an immunoassay method involves high technology and may be costly, once the specific antibody is available and the method has been optimized and validated, immunoassay can provide many analyses at a throughput rate and cost much improved over those of conventional approaches. Many immunoassay methods, namely homogeneous, allow the analysis of the macromolecule bound fluorophore in the presence of the free fraction, without separation, even when both emit in the same spectral region. The analyte concentration in a sample can be monitored directly from the reaction mixture through its effects of the fluorescence properties of the labeled antigen or antibody. Thus, the assays are very rapid and simple (one incubation and no washing), and their development has been among the main objectives in fluoroimmunoassay research. However, the sensitivity of homogeneous assays is often seriously limited by interferences from samples (serum) and by the low degree of fluorescence change (quenching, enhancement, polarization, energy transfer) in an immunoreaction. Polarization fluorescence immunoassay (PFIA) is a homogeneous one. The method basis is that haptens labeled with a fluorophore and irradiated with polarized light emit light of greater polarization if the hapten is bound to an antibody rather than free in solution. The advantages of this technique as a means of measuring analytes in serum were outlined in original publications

Determination of organochlorine pesticides in apple samples by differential-pulse polarography in emulsified medium

The determination of the organochlorine pesticides dieldrin, heptachlor, α-endosulfan, β-endosulfan and endosulfan sulphate and their mixtures in spiked apple samples was carried out in oil-water emulsions formed with ethyl acetate and a mixture of Hyamine 2389 and Triton X-405. Extraction of the pesticides from the apples was accomplished using x-hexane. Clean-up of the extract and fractionation was carried out with a Florisil column, using n-hexane and n-hexane-ethyl acetate (20:1) as eluents. The recoveries for each pesticide individually were about 90% for heptachlor, endosulfan sulphate and both isomers of endosulfan and about 70% for dieldrin at concentration levels of 0.37, 0.93 and 1.27 μg g −1 of apple for heptachlor, dieldrin and endosulfan sulphate, respectively, and 1.22 μg g −1 for each of the endosulfan isomers. Similar results were obtained with binary and ternary mixtures and with a mixture containing all the pesticides studied, indicating the validity of the extraction and separation method developed.

Residue determination of the plant growth regulator naphthylacetic acid in spiked apple samples

1-Naphthylacetic acid (NAA) residues in apples have been determined by direct, first and second derivative spectrofluorimetry, without need for cleanup procedures. The experimental variables and instrumental parameters have been studied. A detection limit of 1.1 ng/ml was achieved with the first derivative approach. Recoveries of NAA from spiked apple samples ranged from 96.7 to 99.2%.